Tungsten concentrates are converted to sodium tungstate solution by digestion in sodium hydroxide or sodium carbonate or by pressure leaching with sodium hydroxide or sodium carbonate. The resulting sodium tungstate solution is then purified and converted to ammonium tungstate via a tungsten solvent extraction system. The ammonium tungstate solution is then subjected to an evaporation process to precipitate ammonium paratungstate which is the precurser of pure tungstic oxide, which can be reduced to tungsten metal.
The above process typically results in recovery of about 85% of the tungsten from the ammonium tungstate solution. The other 15% remaining in the ammonium paratungstate mother liquor is recycled back to the start of the process, that it, the caustic digestion, etc.
Therefore, a process which eliminates the recycling of this remaining 15% through the entire process would be an advancement in the art.